1. Field of the Invention
The present invention relates to a technology for routing a packet.
2. Description of the Related Art
As a network such as a Local Area Network (LAN) to connect multiple terminals, a wired LAN, which is constructed by using cables as transmission paths, are commonly used. Recently, however, networks that are constructed by using electromagnetic waves, instead of cables, as transmission paths are increasingly used. Public line networks of mobile phones and Personal Handyphone Systems (PHS) that can be remotely connected are examples of such networks.
The public line network does not require cables, which allow terminals to freely move and easy connection to the mobile terminals. However, the bandwidth of the public line network is smaller as compared to that of the wired LAN, and communication speed is slow.
To overcome the aforementioned drawback, a conventional technology is disclosed in “Provision of a communication line sharing system that uses a mobile Internet Protocol (IP)” by Hidetoshi Muramatsu, Qiang Fu, Susumu Ishihara, and Tadanori Mizuno, papers presented at 64th National Conference of Information Processing Society of Japan (3), pp. 3-565 to 3-566, Mar. 2002. In the conventional technology, based on Mobile IPv4 [RFC3344], a virtual path is formed with bandwidths used by other terminals nearby to connect to an external network, and bandwidth is secured by distribution and accumulation of packets at a Home Agent (HA). This allows a terminal to perform communication through a wider bandwidth path compared to when the terminal uses only its public line network.
However, the conventional technology requires IP tunneling based on mobile IP at the HA that carries out distribution and accumulation of packets in the upstream of the public line network as well as IP tunneling to transfer a packet to another terminal nearby. Such IP tunneling results in packet header overhead.
To be specific, when a terminal on a LAN transmits a packet via another terminal to a communication partner (hereinafter, “Correspondent Node (CN)”) outside the LAN, the packet has to be encapsulated for IP tunneling based on mobile IP and also encapsulated for IP tunneling to transfer the packet from the terminal to the other terminal. That is, the packet is repeatedly encapsulated.
Sufficient regulations have not been established for security of mobile IP, and, for example, to ensure security of the VPN, further encapsulation is required for VPN IP-tunneling, which further increases packet header overhead. In other words, ensuring of security and reduction of packet header overhead are in a trade off relation.